1. Field of the Invention
The present invention relates to a continuous casting nozzle used for continuous casting of steel, in which a plurality of metal bars are embedded inside at least one portion of a refractory material forming a nozzle main body including a neck portion, a middle portion, and a lower portion.
2. Description of Related Art
Conventionally, there is known a long nozzle for casting molten steel from a ladle without exposing the molten steel to the open air so as to prevent the molten steel from being secondarily oxidized. Recently, the capacity of a tundish, i.e., a molten steel receiving vessel, becomes larger in order to improve a quality of steel in the continues casting. Together with this trend of the tundish, a shape of the nozzle becomes larger and heavier. Furthermore, the nozzle is not discarded after a single continuous casting, but is used throughout multiple castings or reused. Thus a service life of the nozzle is improved. As a result, a required material for manufacturing the nozzle is substantially reduced. In general, an immersion nozzle is employed between the tundish and the mold to cast steel. The long nozzle has such shapes as shown in FIG. 8. FIG. 8 shows a straight type long nozzle (A) and a wide lower type long nozzle (B) which are respectively designed to satisfy a required quality of steel and practically used.
Since the long nozzle used for continuous casting is used for casting molten steel without exposing the molten steel to the open air so as to prevent the molten steel from being secondarily oxidized, the penetration of the open air caused by such phenomena as erosion, crack, breakage or the like during casting brings disastrous damage to the quality of steel. However, the long nozzle has a various kind of complex shapes in addition to the shapes as shown in FIG. 8, thus lowering the structural strength of the nozzle to cause breakage in the middle portion or neck portion of the long nozzle. On the other hand, the service life of the long nozzle has been improved, and the long nozzle is intended to be used throughout multiple castings. When the long nozzle is used throughout multiple castings, the inner surface of the long nozzle is eroded, or the outer surface of the long nozzle is oxidized, thus the thickness of the long nozzle is made thinner. As a result, the structural strength of the nozzle is lowered to cause breakage in the vicinity of the neck portion of the nozzle main body.
Furthermore, the following properties as the material of the long nozzle are required:
(1) excellent thermal shock resistance to the rapid heat at the time when the casting is started;
(2) large mechanical strength to prevent breakage and breakdown of the nozzle from occurring during casting;
(3) excellent erosion resistance to molten steel, slag or the like;
(4) excellent oxidization resistance.
There is not found a refractory to fully satisfy the above mentioned requirements, as yet. Since an aluminum graphite refractory partially satisfies the above mentioned requirement, the aluminum graphite refractory is frequently used according to the purpose and condition of the nozzle. However, when the long nozzle is broken and fallen at the time of starting the casting or during casting due to the thermal shock according to the rapid heat, the shortage of the mechanical strength, the erosion according to molten steel or slag, or progressive oxidation of the nozzle, the molten steel is splashed over operators working on the casting floor to cause a serious damage such as threatening life of the operators.
In order to solve the above mentioned problem, there are studied and practiced various kinds of means to settle the problem such that the shape of the nozzle is developed, or that the thickness of the nozzle is increased, but those means do not come to decisively solve the problem.
As one of the means to settle the problem, the steel plate is wound up around the outer surface of the neck portion of the nozzle main body to reinforce the strength of the nozzle. FIG. 7 shows a conventional nozzle in which the steel plate is wound up around the outer surface of the neck portion to reinforce the strength of the nozzle. As shown in FIG. 7, a metallic shell 104 is provided in the vicinity of neck portion in the upper portion of the long nozzle 103 to protect the refractory main body. Since the long nozzle is pushed upward from the lower side by a supporting device 105 to fit the long nozzle 103 to the lower nozzle 102 of the ladle 101, the metallic shell disfigures or deteriorates due to the heat and is lifted upward, thus the outer peripheral portion of the long nozzle at the lower end of the metallic shell is progressively oxidized. The long nozzle reached under the above condition is broken or damaged by the vibration caused by the molten steel flowing through the inner bore of the nozzle during casting or the shock caused by the falling of the molten steel at the beginning of the casting, thus casing disastrous damage.
Accordingly, an object of the present invention is to provide a continuous casting nozzle in which the strength of the neck portion and the lower portion is enhanced, there is no danger of cracking and breaking, high-quality steel can be supplied steadily, the safety during operation can be ensured, and the cost of refractories can be reduced.
To solve the above problems, the inventors of the present invention have intensively studied. As a result, it was found that a continuous casting nozzle can be provided in which cracking and breaking of the nozzle can be prevented to ensure a required strength, a raw refractory material can be charged uniformly in molding the nozzle, and the cost can be decreased by embedding a plurality of metal bars at least along the longitudinal direction of a nozzle main body in at least one portion inside a refractory material forming a nozzle main body including a neck portion, a middle portion, and a lower portion. Further, it was found that when the metal bars are embedded along the longitudinal direction of the nozzle main body without embedding stainless steel bars in an annular form, substantially the same strength as that of the nozzle provided with stainless steel bars embedded in an annular form can be obtained. The present invention was made on the basis of the above-mentioned findings.
The first embodiment of the continuous casting nozzle of the invention comprises a nozzle main body including a neck portion, a middle portion and a lower portion, made of refractory material, having an inner bore through which molten metal flows; and a plurality of metal bars embedded inside said neck portion both in a vertical direction and a horizontal direction.
In the second embodiment of the continuous casting nozzle of the invention, a ratio of outer diameter of said metal bar embedded in a vertical direction to outer diameter of said metal bar embedded in a horizontal direction is within a range from 3/1 to 15/1.
In the third embodiment of the continuous casting nozzle of the invention, said plurality of metal bars embedded in a horizontal direction are embedded in said neck portion of said nozzle main body within an area ranging from at least 5 cm above a point in which an inclined surface of said neck portion intersects a vertical surface thereof to at least 15 cm below said point.
In the fourth embodiment of the continuous casting nozzle of the invention, said plurality of metal bars are embedded in a thickness direction of said neck portion within a range of at least 1.5 cm from a surface of said inner bore.
The fifth embodiment of the continuous casting nozzle of the invention comprises a nozzle main body including a neck portion, a middle portion and a lower portion, made of refractory material, having an inner bore through which molten metal flows; and a plurality of metal bars embedded inside of at least one portion of said refractory material forming said nozzle main body along a longitudinal direction thereof.
In the sixth embodiment of the continuous casting nozzle of the invention, said plurality of metal bars are embedded inside an area of said nozzle main body ranging from said neck portion through said middle portion to said lower portion.
In the seventh embodiment of the continuous casting nozzle of the invention, said plurality of metal bars are embedded inside vicinity of said neck portion of said nozzle main body.
In the eighth embodiment of the continuous casting nozzle of the invention, said plurality of metal bars are embedded inside said lower portion of said nozzle main body.
In the ninth embodiment of the continuous casting nozzle of the invention, said plurality of metal bars comprise a first metal bars embedded inside said neck portion of said nozzle main body and a second metal bars embedded inside said lower portion of said nozzle main body.
In the tenth embodiment of the continuous casting nozzle of the invention, said first metal bars embedded inside said neck portion and said second metal bars embedded inside said lower portion respectively extend to said middle portion of said nozzle main body, and are overlapped in said middle portion.
In the eleventh embodiment of the continuous casting nozzle of the invention, said plurality of metal bars are embedded at nearly regular intervals.
In the twelfth embodiment of the continuous casting nozzle of the invention, a cross sectional area of said plurality of metal bars comprises a round, oval, polygonal, or pentacle shape.
In the thirteenth embodiment of the continuous casting nozzle of the invention, a metal net is embedded together with said plurality of metal bars.